1. Field of the Invention
The present invention relates to an exposure adjusting apparatus, an image normalizing apparatus and an image normalizing method, and particularly relates to an exposure adjusting apparatus, an image normalizing apparatus and an image normalizing method which can adjust the exposure parameter via variable adjusting amounts.
2. Description of the Prior Art
Since the image digitalizing technique improves, the electronic apparatus utilizing the digital image such as a digital camera, a video camera and an optical mouse are developed and become popular. Such product always includes an image sensor, which can catch an image for the electronic apparatus. Also, the image sensor can adjust the exposure parameter of the image sensor according to an exposure amount of the image, to adjust the exposure amount of the image such that the image won't be overexposed or underexposed (i.e. the brightness is too high or too low).
FIG. 1 is a circuit diagram illustrating a prior art CMOS image sensor. As shown in FIG. 1, the image sensor 100 includes a pixel array 101, a signal reading circuit 103, an amplifier 111 and an analog to digital converter 113. The pixel array 101 includes a plurality of pixel units PIX11-PIXnm. If the image sensor 100 wants to read an image, the signal reading circuit 103 reads pixel signals in the pixel array 101, and then the amplifier 111 amplifies the pixel signal. After that, the analog to digital converter 113 transfers the pixel signal to a digital form, such that the following digital signal processor 115 can process the digitalized pixel signal. The signal reading circuit 103 has a plurality of signal reading units SR1, SR2 and SR3, for reading pixel signals from the pixel units PIX11-PIXnm.
FIG. 2 is a circuit diagram illustrating the pixel array 101 shown in FIG. 1. The cross voltage of a photo diode PD is charged to Vrst if the reset signal RES controls the NMOS M2 to be conductive. The signal reading units SR1, SR2, SR3 in the signal reading circuit 103 all include an energy storing device. If the NMOS M3 is controlled to be conductive via the pixel selecting signals RSEL1 or RSEL2, the cross voltage of the photo diode PD is transformed to a current via the NMOS M1, and the current is stored to the energy storing devices in the signal reading units SR1, SR2, SR3. By this way, the charge stored by the energy storing devices of the signal reading units SR1, SR2, SR3 indicate the light amount sensed by the corresponding pixel. The illumination intensity and illumination time for the light sensed by the photo diode PD can be regarded as exposure intensity and exposure time of the photo diode PD. The exposure amount of the pixel unit is generated vian exposure intensity×exposure time. Additionally, a mean value for the exposure amount of all pixel units can be regarded as exposure amount of a whole image. Accordingly, if the exposure amount of the image is desired to be in a predetermined exposure range, illumination intensity and illumination time for the light sensed by the photo diode PD (i.e. the exposure parameter) can be adjusted to change the exposure intensity and the exposure time of the image.
In the prior art, the step of adjusting the exposure parameter always adjusts the exposure parameter for a fixed value per time. For example, if the exposure parameter is 100 units and the image exposure amount is too large, then the exposure parameter decreases for 10 units and the new exposure parameter is utilized to catch an image. However, if the exposure parameter is 1000 units but still decreases for 10 units per time, the exposure parameter decreases too slowly and the exposure parameter must be adjusted for many times to control the exposure amount of the image to fall in the desired range. On the contrary, if the exposure parameter is 100 units but decreases for 40 units or more per time, the exposure time is uneasy to be adjusted to the desired range.